As will be appreciated by those skilled in the art, a charge pump can be characterized as a circuit that uses capacitors to create either a higher or lower voltage. Charge pumps are used in a variety of different applications such as, for example, applications involving Delay Locked Loops (DLLs) and Phase-Locked Loops (PLLs).
With respect to PLLs, a charge pump can be used to provide a control voltage applied to a Voltage Controlled Oscillator (VCO). Typically, a PLL includes a phase detector, a loop filter coupled to the output of the charge pump, an amplifier, and a VCO interconnected in a known manner to form a feedback system. The charge pump converts logic level pulses generated by the phase detector into current pulses which are fed to the loop filter. The loop filter integrates the current pulses to produce a control voltage for the VCO.
With respect to DLLs, a charge pump can be used to provide a control voltage for a Voltage Control Delay Line (VCDL) of the DLL. As will be appreciated by those skilled in the art, in certain types of devices (for example, DRAM devices) a DLL can be used to change the phase of a clock signal. In this regard, a DLL includes a delay chain composed of number of delay gates connected in series (in a daisy chain manner).
Thus the charge pump is an important component in PLLs and DLLs, and many issued patent are directed towards them. One such patent is U.S. Pat. No. 7,092,689 of Boecker et al. which discloses a charge pump including a first array of mirror devices for producing, within the charge pump, a positive delta current, and a second array of mirror devices for producing, within the charge pump, a different delta current. Each mirror device in either of the arrays has current mirrored into it from a different reference current source, and the phase shift producing currents generated by the arrays do not track the charge pump current. As a result, trying to calculate the effects of the arrays under actual operating conditions based upon the conditions existing at testing/calibration time is difficult.
Accordingly, it would be advantageous to improve upon charge pump circuits that facilitate phase shifting in a DLL or PLL.